At present, the resin products for the automobile inner and outer package containing polypropylene resins, having a product wall thickness of 2 mm or more predominate. For example, frequently, an instrument panel has a thickness of around 3 mm, a bumper has a thickness of 2.5 to 3.5 mm and other inner package products have a thickness of 2.2 to 3 mm. Accordingly, even a melt flow rate (MFR) at 230° C. under 21.2 N is 30 g/10 min or less as the fluidity and a flexural modulus at 23° C. is 2,500 MPa or less as the rigidity, the requirements for the physical properties of a polypropylene resin composition used in the above resin products can be sufficiently satisfied.
However, recently, particularly in the field of the automobile inner and outer package resin products, in order to contribute to the global environment such as CO2 reduction, from such a viewpoint that the reduction of the total used amount of the resin is important, as one measure therefor, further thinning of a resin product is required. Polypropylene resin compositions having the above physical properties cannot respond to thinning of the resin products.
Here, although polypropylene resin compositions in which the physical properties such as the rigidity are enhanced are described in Patent Documents 1 to 8, it is considered that even such polypropylene resin compositions cannot sufficiently respond to thinning of the resin products for the automobile inner and outer package containing a polypropylene resin.
[Patent Document 1]
    Japanese Patent Application Publication No. JP-A-8-302108[Patent Document 2]    Japanese Patent Application Publication No. JP-A-9-87481[Patent Document 3]    Japanese Patent Application Publication No. JP-A-7-33919[Patent Document 4]    Japanese Patent Application Publication No. JP-A-9-71712[Patent Document 5]    Japanese Patent Application Publication No. JP-A-10-324725[Patent Document 6]    Japanese Patent Application Publication No. JP-A-11-189700[Patent Document 7]    Japanese Patent Application Publication No. JP-A-9-124857[Patent Document 8]    Japanese Patent Application Publication No. JP-A-8-134288
On the other hand, it is known that it is an effective means for enhancing the rigidity and the impact resistance of a polypropylene resin composition to mix fine particle-shaped (average particle diameter: less than about 1 μm) talc in the composition. However, since a particle-shaped talc is obtained by repeating steps of grinding and classifying talc produced in the shape of a bulk or the like, the smaller the particle diameter thereof is, the more the number of repeating the steps of grinding and classifying is, so that the unit price of talc becomes high. Accordingly, the amount of talc which can be added in an article of utility, such as an automobile inner and outer package resin product is limited in terms of the cost.
In addition, it is proposed to enhance the rigidity and the impact resistance by dynamically crosslinking an elastomer component blended in a polypropylene resin composition by adding a crosslinker or the like (Patent Document 9). However, it is considered that even this polypropylene resin composition cannot sufficiently respond to the thinning of resin products for the automobile inner and outer package containing a polypropylene resin.
[Patent Document 9]
    Japanese Patent Application Publication No. JP-A-7-304910